1. Field of the Invention
The present invention generally relates to a biosignal detecting apparatus which executes communications by using a human body as an antenna.
2. Description of the Related Art
Recently, a very short distance radio communication network has been proposed in the fields of medical services and healthcare. This network is called a BAN (body area network), and communications standards of the BAN have been proposed in which a body embedded type instrument or a wearable type instrument is used in the BAN.
In addition, conventionally, instead of using the BAN, technologies using a human body as an antenna have been proposed. For example, an apparatus is disclosed in Patent Document 1. In the apparatus, an electric signal corresponding to human body information is detected from the skin part of a human body, the detected signal is converted into a high frequency signal, and the high frequency signal is transmitted to another apparatus by using the human body as the antenna.    [Patent Document 1] Japanese Laid-Open Patent Application No. 5-317278
However, the human body has a property of absorbing electromagnetic waves (radio waves), and when the human body is used as an antenna, a loss of the electromagnetic waves occurs and the electromagnetic waves may be changed. In addition, conditions for obtaining impedance matching between the apparatus and the human body are changed depending on a relationship between a wavelength of a used electromagnetic wave and the body height of a person or positions of electrodes attached to the human body. Especially, the conditions for obtaining the impedance matching are remarkably changed when the human body is moved.
However, conventionally, when the human body is used as an antenna, the impedance matching between the human body and the apparatus has not been obtained under conditions where elements such as a loss of the electromagnetic waves to be transmitted and a body height difference among individuals are assumed.